1. Field of the Invention
The present invention relates to a receiver for receiving a high-definition signal, and more particularly, to a circuit and a method each for generating a field identification signal using a field synchronous signal.
2. Description of the Related Art
By virtue of research and development for achieving a large-sized and high-definition screen, Japan is carrying out the first high-definition television (HDTV) broadcasting on the basis of multiple subnyquist sampling encoding (MUSE) as a current analog transmission method. The U.S.A. has proposed a grand alliance (GA)-HDTV system, and for this, has adopted a vestigial side band (VSB) modulation method, being a digital transmission method. The GA-HDTV uses an 8-VSB using 8 levels, for a terrestrial broadcast mode, and a 16-VSB using 16 levels, for a high speed cable mode.
FIG. 1 shows a VSB data frame format of the GA-HDTV. The VSB data frame is comprised of two fields each comprised of a field synchronous segment and 312 data segments. Each data segment is comprised of 4 segment synchronous symbols and 828 data symbols. The segment synchronous symbols are inserted into an 8-level digital data stream at the head of the field synchronous segment and each of the data segments. The respective 4 segment synchronous symbols are formed in a constant pattern having a signal level of "+5, -5, -5, +5", and the remaining data of each data segment are randomly formed having an arbitrary signal level among the 8 levels (.+-.1, .+-.3, .+-.5, .+-.7).
Meanwhile, each field synchronous signal sequence (FIELD SYNC #1 and FIELD SYNC #2), for representing the start of each field, is inserted into the field synchronous segment corresponding to the first segment for each field. FIG. 2 shows the format of a VSB data field synchronous signal. Referring to FIG. 2, the field synchronous segment is comprised of 832 symbols. The first four symbols among them are segment synchronous symbols. A 511 pseudo number (PN) comprises the next 511 symbols, and three PNs each of 63 symbols comprise the following 189 symbols, and the other information comprises the remaining 128 symbols. Here, the PN511 has a predetermined signal sequence which is represented by levels +5 and -5, so that it is used in a signal processing block using a known signal sequence, such as an equalization. The second 63PN of the three 63PNs has a phase which is inverted in every alternate field. In this way, a field synchronous signal sequence indicating the start of each field having a format shown in FIG. 2, is inserted into a first segment in each field, and the field synchronous signal sequence is a known signal sequence having a constant form.
Accordingly, a synchronous signal must be detected by a receiver, to reproduce a transmitted VSB signal having the same structure as that of FIG. 1. Furthermore, the receiver must determine whether a field is an odd or even field, for correct reproduction to be possible. In particular, an equalizer and an error correction decoder in a receiver, necessarily require a field identification signal in order to accomplish a correct signal processing.
Meanwhile, circuits for generating a field identification signal applied in an analog television have been proposed. However, since the GA-HDTV has a different signal format to analog television, and processes entire signals digitally, it was impossible to apply the field identification signal generating circuit for the conventional analog television to the GA-HDTV without making changes.